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The reflectance database

All reflectance measurements in ore microscopy are of low value without data to compare to. The most comprehensive work on reflectance data is still the Quantitative Data File for Ore Minerals, 3rd edition (QDF3) from A. J. Criddle and C. J. Stanley, published in 1993. Some of the gaps there are filled by the Atlas of ore minerals (Picot, P., Johan, Z.; B.R.G.M., 1982) which was published earlier as the QDF3 but data were for unknown reason not consolidated although it contains data of the more rare minerals. Interestingly, one of the earlier versions of the QDF was available as a computer program, but was not maintained and disappeared many years ago. The QDF3 lacks therefore some major points: data comparison in numbers or graphically is not possible and neither is searching of course. The QDF3 is now over 20 years old and outdated.

To overcome these issues, a new ore mineral database was build which contains 95% of the data from the QDF3 plus a majority of published reflectance data from the main mineralogical literature with focus on opaque minerals. The database now contains 1065 datasets with reflectance values ranging from at least 440-700 nm. Incomplete sets were excluded but some interpolation of data was performed when the standard wavelength were not used. Datasets can be compared and sorted in tables or as diagrams, and for each field (i.e. wavelength) complex search terms can be applied. A search like 400nm: > 50%; 440 nm: 31-34%; 600nm: < 23.1% and Fe in the chemical formula can be performed in seconds. Searches based on elements are of course also possible. Recently I added also those minerals to the database of which reflectances only the IMA-COM wavelength are available.

The latest addition to the functionality of the database is the calculation of the color values x, y, Y, λd and Pe. Except for the dominant wavelength, the color values are calculated from the reflectance spectrum in real-time. The calculation of the dominant wavelength is more complicated and runs with a script. All color values are presented in a chart, if needed in comparison with other minerals.

Single dataset:


Graphical comparison:


A graphical comparison can be useful as shown by this example. Gold without and with 3.6 and 11.6% silver:


For more datasets, graphics become unreadable, therefore tables are easier to handle. Table, sorted for 500nm:


And the latest part, the color values:



The database grows of course and functionality is added as needed. And before you ask: the database is not available for free. Programming the software, acquiring and entering the datasets needed hundreds of hours taken away from family, life and making money. Besides that, the copyright status of the QDF3 is unclear. Building this database is legal, distributing it might not. If you are seriously interested in this work, drop me an email.